A professor scoured the seas for the heartiest, fastest-growing algae to help poor nations develop a seaweed crop for carrageenan — the gelatinous emulsifier used in products ranging from toothpaste and shoe polish to nonfat ice cream.

The late Maxwell Doty succeeded, in one regard. His research helped the Philippines and other island nations establish multimillion-dollar industries to supply carrageenan to the food, beverage and cosmetic industries.

Yet his efforts also left an unwanted legacy. Open-cage experiments inoculated Hawaiian coastal waters with a half-dozen types of foreign algae. These aggressive invaders have smothered at least half the reefs in Kane'ohe Bay on O'ahu's east coast and have begun to spread to waters beyond.

The sprouting problem has kept professors, graduate students and state officials busy trying to rein in the shaggy mats of thick-stemmed seaweed that threaten coral reefs and the fish, turtles and other sea life that depend on them. After years of trial and error, scientists believe they have arrived at a solution.

It involves a giant underwater vacuum they call the Super Sucker.

On a recent Sunday, a pair of divers ripped chunks of the foot-thick blanket of algae from atop a coral reef and fed it into a fat hose. The suction is created by a special vacuum pump that doesn't damage any animals inadvertently scooped up or chop the algae into bits, which could make the effort futile. Even small seaweed fragments flushed back into the water would simply reseed the reef.

On a barge above the divers, Cynthia Hunter sifted through the piles atop tight-mesh screens to remove any animals accidentally vacuumed up. She then bagged the seaweed to be taken ashore for composting and use as fertilizer in agricultural fields.

"It's pretty clean work," said Hunter, a biology professor. She showed that only a few bits of coral ended up in the glistening mix of golden-green seaweed.

Yet it's also a slow and tedious task, even though the Super Sucker can scoop up about 800 pounds of algae an hour.

No one knows that better than Eric Conklin, who holds a doctorate in zoology. He has spent hours and hours feeding clumps of "gorilla ogo" and "smothering seaweed" and other types of invasive algae into the Super Sucker.

"If all we were doing is vacuuming the reef, it would come back and we'd be back at it again," Conklin said. "Our plan is to knock back the growth so it won't spread and (to) give our long-term solutions a chance to take hold."

The hopes of long-term solution rest largely on the sea urchin, a softball-size creature with hard, sharp spines. They eat the invasive algae. One of the problems is that the populations of urchins around Hawaii have plunged because of excessive harvesting. They are collected for their gonads, prized by sushi-bar patrons.

University researchers are learning how to propagate one species, called the collector urchin, at the lab on Coconut Island so that they can scatter baby urchins on freshly vacuumed reefs.

"The urchins can do the much harder, tedious work of grazing the little bits of algae," said Celia Smith, a botany professor.

The strategy has worked in small test plots, where thumb-size nubs of corals have rebounded. Now the university, working with The Nature Conservancy and Hawaii's Department of Land and Natural Resources, is scaling up the program to attack the invaders one reef at a time.

Researchers here have sought a gentle approach, given what lies beneath the interwoven mats of smothering algae and gorilla ogo, which go by the scientific names Eucheuma denticulatum and Gracilaria salicornia.

Coral reefs around the world are struggling from a combination of assaults besides the extra-warm water that causes coral bleaching. Decades of overfishing have removed fish and other animals that keep overgrowth of algae in check. And excessive plant food — nitrogen and phosphorus compounds — is spilling into reefs because of runoff from agricultural fields and effluent spewing from sewer pipes.

The resulting algal overgrowth shades coral reefs and colonies of tiny animals that need sunlight to survive. It also promotes the spread of harmful bacteria and various types of infections.

Smith, the university's botanist, calls it "one of life's rich ironies" that she has spent so much of her career trying to protect corals from something unleashed by her former professor, Maxwell Doty. Smith was hired in 1988 to take his job as the university's algae specialist.